Exposure to cigarette tar inhibits ribonucleotide reductase and blocks lymphocyte proliferation

Cigarette smoking causes profound suppression of pulmonary T cell responses , which has been associated with increased susceptibility to respiratory tr act infections and decreased turner surveillance. Exposure of human T cells to cigarette tar or its major phenolic components, hydroquinone and catech ol, causes an immediate cessation of DNA synthesis without cytotoxicity. Ho wever, Little is known of the mechanisms by which this phenomenon occurs. I n this report we demonstrate that hydroquinone and catechol Inhibit lymphoc yte proliferation by quenching the essential tyrosyl radical in the M2 subu nit of ribonucleotide reductase.